JPH05328586A - Method of automatically monitoring analog input circuit - Google Patents

Abstract

PURPOSE:To materialize maintenance free by using the signal attained by operating the output of a filter, which has property equivalent to the transfer function of an analog filter, into a digital numeric value, receiving the signal obtained by converting the analogous quantity of electricity into digital not through an analog filter. CONSTITUTION:The signal on the quantity of electricity in a system is introduced from a transformer PT or a current transformer CT into an input converter 1. This input signal is input into a sample-and-hold circuit 3a through an analog filter 2, and is also input into a sample-and-hold circuit 3b not through an analog filter, and is converted into digital quantity with a multiplexer 4 and an A/D converter 5, respectively, and then, is stored in a RAM6. And, CPU 8 checks the accuracy of an analog circuit by detecting the relative error between the signal being operated from a signal, which is converted into digital not through a filter, into a digital numeric value after passing the filter having the property equivalent to the transfer function of the filter 2 and the signal being converted into digital through the filter 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for automatically monitoring an analog input circuit of a digital protective relay that performs an analog / digital conversion of an alternating current electric quantity to perform a protective operation.

[0002]

2. Description of the Related Art A digital protective relay introduces AC electricity such as voltage and current from an electric power system through an input converter to convert an AC analog signal into a digital signal.
It is used for protection calculation with a digital processing device such as a microcomputer, and it has been widely applied to protect power systems because it can realize a high-performance and highly reliable protection relay due to its excellent calculation processing capability and accident diagnosis capability. There is. Figure 6
Is a diagram showing the general configuration of the analog input circuit and digital operation part of the digital protection relay. The system electricity quantity is introduced from the transformer PT or current transformer CT of the system to the input converter 1 and is a level that can be handled by an electronic circuit. Convert to. Next, the system electricity quantity is converted from an analog quantity to a digital quantity. First, in order to remove the high frequency component that causes an error, it is input to the analog filter 2 and a frequency component of 1/2 or more of the sampling frequency determined by the sampling theorem Dampen enough.
The analog filter output is the sample and hold circuit (S /
H) 3, multiplexer (MPX) 4, analog-to-digital converter (A / D) 5 converts into a digital amount at every predetermined sampling period, and temporarily stores it in a random access memory (RAM) 6 and then It is used for the protection operation of the digital operation processing unit (CPU) 8 according to the operation program of the read only memory (ROM) 7.

The mission of the protective relay requires a high degree of operational reliability, but the digital protective relay of the above construction realizes most of the protective function by software, and therefore, there is little change over time in this portion, so it is reliable. It is highly likely. But,
The analog input circuit, which consists of analog filters and analog-digital converters, uses operational amplifiers, resistors, and capacitors. If the characteristics of these elements change, the error in the analog input circuit increases and the performance of the protective relay increases. Directly affect. For this reason, conventionally, the analog input circuit performs the accuracy check by automatic monitoring. As is well known, automatic monitoring of an analog input circuit includes constant monitoring and automatic inspection. Electric Cooperative Research "Digital Relay", No. 41
Vol. 4, No. 4 (1986), a typical method of constant monitoring is to detect imbalance between phase inputs.
There is a method of Eq. (1) and a method of Eq. (2) that detects the occurrence of zero-phase components by applying the symmetric coordinate method. For automatic inspection, apply a known inspection input signal to the analog input circuit,
There is a method of comparing the value of the signal converted into a digital amount with a preset theoretical value of the inspection input signal, and determining the quality based on the difference. max {I _Y } ≧ α · min {I _Y } + β (1) max {I _Y }: Input of the maximum phase of each phase. min {I _Y }: Input of the minimum phase of each phase. α, β: constants. _{| I R + I S + I} T -3I O | ≧ ε 1 .................. (2) I R, I S, I T: phase input. I _O : Zero phase input. ε ₁ : Sensitivity term.

[0004]

In order to maintain the operation reliability of the protective relay and realize maintenance-free operation, the automatic monitoring of the analog input circuit requires a highly accurate detection performance that can guarantee the performance of the protective relay. It is desirable to have. For this purpose, the detection sensitivity of the automatic monitoring may be set to the same level as the error guarantee value of the protective relay in which the inherent error of the analog circuit is dominant. However, in the above-mentioned conventional automatic monitoring system, system phenomena such as unbalance of system electricity quantity and frequency fluctuation,
Inspection error of automatic inspection Since the error that occurs due to the adjustment accuracy of the input signal itself or the secular change cannot be distinguished from the inherent error of the analog input circuit, the detection sensitivity is set so that automatic monitoring failure is not unnecessarily detected due to these error factors. I have no choice but to set it low. Therefore, the accuracy of the protective relay cannot be guaranteed only by automatic monitoring, and in order to perform the accuracy check of the analog input circuit more strictly, the strain-free AC input for testing should be connected to the relay on occasions such as periodic inspections. It was necessary to perform human work to measure the operating values of the protective relay with a meter that was applied and calibrated and managed. This is one of the factors that hinder maintenance-free digital protection relays. The present invention has been made to solve the above problems,
It is an object of the present invention to provide a highly accurate automatic monitoring method of an analog input circuit that can guarantee the accuracy of a protective relay without adding complicated hardware and realizes maintenance-free operation.

[0005]

The structure of the present invention will be described with reference to the structure diagrams of FIG. 1 and FIG. 2 corresponding to the embodiments. The analog input electric quantity is analog-to-digital converted through an analog filter. The obtained digital signal and the digital signal obtained by analog-to-digital conversion of the analog electric quantity without passing through the analog filter are input, and the filter output having the characteristics equivalent to the transfer function of the analog filter is digitally numerically operated. Using the obtained signal, the relative error between the two is detected to check the accuracy of the analog input circuit.

Therefore, it is possible to guarantee the accuracy of the protective relay without requiring complicated automatic monitoring hardware, and without being affected by the influence of the system side, the adjustment error of the automatic monitoring circuit, and the secular change. It is possible to provide an accurate automatic monitoring system for analog input circuits.

[0006]

Embodiments will be described below with reference to the drawings. Figure 1
FIG. 1 is a configuration diagram of an embodiment for explaining an automatic monitoring system of an analog input circuit according to the present invention. In FIG. 1, the same parts as those in FIG. 6 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 1, the system electricity quantity is introduced into the input converter 1 from the transformer PT and the current transformer CT. One of these input signals is input to the sample hold circuit 3a via the analog filter 2 for removing high frequency components, and the other input the same input signal to the sample hold circuit 3b without passing through the analog filter. The multiplexer 4 and the analog / digital converter 5 are configured to convert into a digital amount at a predetermined sampling period and store the digital amount in the random access memory 6.

FIG. 2 is a functional block diagram for explaining the automatic monitoring process by the software of the present invention. The input signal 9a is shown in FIG.
The input signal 9b is a signal which is digitally converted through the analog filter 2 of FIG. 1 and the input signal 9b is a signal which is digitally converted without passing through the analog filter of FIG. The input signal 9b is a transfer function H corresponding to the transfer function H (s) of the analog filter 2.
(Z) is input to the digital filter 9, and the filter output is digitally numerically operated. After that, the output signal 10 of the digital filter is input to the comparator 11 together with the input signal 9a to detect the relative error between them, and the accuracy of the analog input circuit is checked. Here, the digital filter is based on the method of processing digital data II
It can be roughly classified into an R (infinite response) filter and an FIR (finite response) filter, but as is well known, in any method, a filter equivalent to an analog filter can be realized by digital numerical calculation in principle. For example, when the transfer function H (s) of the analog filter 2 is generally expressed by the equation (3), the transfer function H (s) of the digital filter 9 can be obtained by using the design method by the impulse response method in order to realize this with the IIR filter.
Equation (4) may be used for (z).

Next, a method of detecting an error between the signal 9a from the analog filter and the output signal 10 of the digital filter 9 by the comparator 11 will be described. When the input signal of the protective relay is f, and the output signal 10 of the digital filter is the reference signal for error detection and equation (5) is used, the signal 9a from the analog filter has a gain error k and a phase error θ (6 ) Is given by the formula. Signal 10 F _D (jω) = Gexp {jω} ……………………… (5) Signal 9a F _A (jω) = G (1 + k) exp {j (ω + θ)}… (6) exp {} Indicates an exponential function. Here, the amplitude value G of the output signal is a value obtained by multiplying the amplitude of the input signal f by the gain of the filter. However, when the ratio of the equations (5) and (6) is calculated, the amplitude value G depending on the input signal is It is erased and the result becomes formula (7). Expression (7) represents the error component of the signal 9a when the output signal 10 is the reference, that is, the gain error and the phase error of the analog filter when the digital filter is the reference. Therefore, the accuracy of the analog filter can be checked by performing a predetermined level detection on the result of equation (7). F _A (jω) / F _D (jω) = G (1 + k) exp {j (ω + θ)} / Gexp {jω} = (1 + k) exp {jθ} ………………………………………… (7) Since the present invention uses the transfer function of the digital filter configured by software to detect the gain error and the phase error of the analog filter as a reference, this reference does not change over time and always has a constant sensitivity. In addition, highly sensitive error detection is possible. Further, the conventional monitoring method could not be applied with a single quantity input, but since the present invention is basically monitored by input unit, there is no restriction in application due to the introduction amount of the protective relay, and the system Also, the unbalanced amount does not affect the automatic monitoring accuracy at all, and since the main part of the present invention is realized by software, special hardware for automatic monitoring is not required, and can be realized by standard hardware of digital relay. The point is also very advantageous for improving reliability.

In the above-described embodiment, the system electricity quantity passing through the analog filter and the system electricity quantity not passing through the analog filter are input to the individual sample and hold circuits, respectively. Introduce the output into one sample and hold circuit
Even if digital conversion is performed and the number of sample and hold circuits is reduced, it is clear that the same effect can be obtained if the comparator 11 makes a determination in consideration of the time difference between the sampling timings of both signals. Further, when there are a plurality of input signals, if a signal that does not pass through an analog filter is input for each input signal, the number of signals to be converted from analog to digital increases, but the number of input signals depends on the sampling period and analog / digital. There are restrictions due to the relationship with the conversion speed of the converter. In this case, a switching circuit 12 is provided as shown in FIG.
The inputs may be automatically monitored sequentially while switching the signals to be digitally converted. Further, the effect of the present invention is not limited to the execution form of the digital filter processing, and even when the digital filter processing is performed in real time, or the input signal data is stored for a predetermined period, and then the digital filter and the error detection are performed. It goes without saying that the same effect can be obtained by the method of sequentially executing the processing of step 1 while dividing it.

Next, another embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing the construction of another embodiment. The analog filter 2 is constructed so that the inspection command circuit 13 can superimpose a predetermined inspection input signal 14 together with the system electricity quantity introduced from the input converter 1. In addition, the inspection input signal 14 applied by the inspection command circuit 13 is configured to be directly input without an analog filter, and both signals are converted from analog to digital. FIG. 5 is a functional block diagram for explaining the automatic monitoring process by the software of the present invention. The input signal 15 is a signal obtained by digitally converting the superposed signal of the system electricity quantity and the inspection input signal of FIG. 4 through the analog filter 2. The input signal 18 is a signal obtained by digitally converting the inspection input signal of FIG. 4 without passing through an analog filter. The input signal 15 is input to the digital filter 16 having the transfer function G (z), the frequency component of the system electricity quantity is attenuated, and the inspection signal component 17 having a different frequency is extracted. On the other hand, the input signal 18 is a transfer function H corresponding to the transfer function H (s) of the analog filter 2.
(Z) and the transfer function G of the digital filter 16
(Z) is input to the digital filter 19 having a characteristic, and the filter output is digitally numerically calculated to obtain the output signal 20. Then the inspection signal component 17 and the output signal 20
Are input to the comparator 11 to detect the relative error between them. Since the method of constructing the digital filter and the method of detecting the error by the comparator are the same as those in the above-mentioned embodiment, the description thereof is omitted. In the present invention, since the inspection input signal is used as a signal for automatic monitoring of the analog input circuit, a current input circuit whose constant input depends on the power flow of the system and a zero-phase input circuit whose input is usually extremely small are also automatically detected. Monitoring is possible. Further, since the adjustment error of the inspection input signal itself and the level fluctuation due to secular change do not affect the detection accuracy, highly accurate automatic monitoring can be performed. In addition,
Since the inspection input signal only needs to be able to extract its frequency component by the digital filter 16, the signal waveform is not limited to a sine wave, and a square wave or the like can be used.

[0011]

As described above, according to the present invention, a digital signal obtained by analog-to-digital conversion of an analog input electric quantity through an analog filter, and an analog electric quantity without an analog filter are used. Check the accuracy of the analog input circuit by inputting the digitally converted digital signal and using the signal obtained by performing digital numerical operation on the output of the filter having the characteristics equivalent to the transfer function of the analog filter and detecting the relative error between them. Since it is configured so that it does not require complicated hardware, it is not affected by the adjustment error of the automatic monitoring circuit, secular change, unbalance of system, etc. It is possible to provide an automatic monitoring system for analog input circuits.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an automatic monitoring system for an analog input circuit according to the present invention.

FIG. 2 is a functional block diagram illustrating a software configuration of an embodiment of an automatic monitoring system for an analog input circuit according to the present invention.

FIG. 3 is a configuration diagram showing an application example of the present invention.

FIG. 4 is a configuration diagram showing an automatic monitoring system of an analog input circuit according to another embodiment of the present invention.

FIG. 5 is a functional block diagram illustrating a software configuration of an automatic monitoring system for an analog input circuit according to another embodiment of the present invention.

FIG. 6 is a configuration diagram of an analog input circuit and a digital arithmetic unit of a conventional digital protection relay.

[Explanation of symbols]

 1 Input Converter 2 Analog Filter 3,3a, 3b Sample and Hold Circuit (S / H) 4 Multiplexer 5 Analog to Digital Converter (A / D) 6 Random Access Memory (RAM) 7 Read Only Memory (ROM) 8 Digital Operation Device (CPU) 9, 16, 19 Digital filter 9a, 9b, 15, 18 Input signal 10, 17, 20 Digital filter output signal 11 Comparator 12 Switching circuit 13 Inspection command circuit 14 Inspection input signal

Claims (2)

[Claims] 1. A digital protection relay for inputting the amount of AC electricity of a power system and performing a protection operation in a digital arithmetic unit, and first means for inputting the amount of AC electricity and obtaining a signal passed through an analog filter, The second means for inputting / outputting the same amount of alternating current as the input of the first means without passing through an analog filter, and the digital signal obtained by analog-digital conversion of the output of the second means are input. The third means for obtaining the output of the filter having the characteristic corresponding to the transfer function of the analog filter of the first means by digital numerical operation, the digital signal of the output from the third means, and the output of the first means And a fourth means for checking the accuracy of the analog input circuit by detecting a relative error with a digital signal obtained by analog-digital conversion. Automatic monitoring method for analog input circuit. 2. A digital protective relay for inputting an AC electricity amount of a power system and performing a protection operation by a digital arithmetic unit, and inspecting a frequency different from the fundamental frequency of the system together with the AC electricity amount of the power system according to an inspection command. First means for superimposing and inputting the inspection signal to obtain a signal that has passed through the analog filter; and second means for inputting and outputting the inspection signal only in response to the inspection command without passing through the analog filter,
A third means for extracting a check signal component by a digital filter from a digital signal obtained by analog-to-digital conversion of the output of the first means, and an analog-to-digital conversion of the output from the second means. The digital signal as input, and the analog filter of the first means and the third filter
Means for obtaining the output of a filter having a characteristic equivalent to a transfer function obtained by integrating the digital filters of the means described above by digital numerical calculation, an output signal of the third means, and a fourth means
Means for checking the accuracy of the analog input circuit by detecting a relative error with the output signal of the means of claim 5, and an automatic monitoring system of the analog input circuit.